Dual wire welding or additive manufacturing system and method

ABSTRACT

A system and method of welding or additive manufacturing is provided where at least two welding electrodes are provided to and passed through a two separate orifices on a single contact tip and a welding waveform is provided to the electrodes through the contact tip to weld simultaneously with both electrodes, where a bridge droplet is formed between the electrodes and then transferred to the puddle.

BACKGROUND OF THE INVENTION Field of the Invention

Devices, systems, and methods consistent with the invention relate tomaterial deposition with a dual wire configuration using a singlecontact tip assembly.

Description of the Related Art

When welding, it is often desirable to increase the width of the weldbead or increase the length of the weld puddle during welding. There canbe many different reasons for this desire, which are well known in thewelding industry. For example, it may be desirable to elongate the weldpuddle to keep the weld and filler metals molten for a longer period oftime so as to reduce porosity. That is, if the weld puddle is molten fora longer period of time there is more time for harmful gases to escapethe weld bead before the bead solidifies. Further, it may desirable toincrease the width of a weld bead so as to cover wider weld gap or toincrease a wire deposition rate. In both cases, it is common to use anincreased electrode diameter. The increased diameter will result in bothan elongated and widen weld puddle, even though it may be only desiredto increase the width or the length of the weld puddle, but not both.However, this is not without its disadvantages. Specifically, because alarger electrode is employed more energy is needed in the welding arc tofacilitate proper welding. This increase in energy causes an increase inheat input into the weld and will result in the use of more energy inthe welding operation, because of the larger diameter of the electrodeused. Further, it may create a weld bead profile or cross-section thatis not ideal for certain mechanical applications.

BRIEF SUMMARY OF THE INVENTION

An exemplary embodiment of the present invention is a welding system andmethod for welding where a welding power supply provides a weldingwaveform to a contact tip assembly having two exit orifices. A wirefeeding mechanism provides at least two welding electrodes to twodifferent channels in the contact tip assembly, where each of theelectrodes passes through their respective the channels and exit thecontact tip assembly through their respective orifices. The weldingwaveform is provided to each of the electrodes by the contact tipassembly for a welding operation.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and/or other aspects of the invention will be more apparent bydescribing in detail exemplary embodiments of the invention withreference to the accompanying drawings, in which:

FIG. 1 illustrates a diagrammatical representation of an exemplaryembodiment of a welding system of the present invention;

FIG. 2 illustrates a diagrammatical representation of an exemplarycontact tip assembly in an embodiment of the present invention;

FIGS. 3A to 3C illustrate diagrammatical representations of a weldingoperation in an exemplary embodiment of the present invention;

FIGS. 4A to 4B illustrate diagrammatical representations current andmagnetic field interactions in exemplary embodiments of the presentinvention;

FIG. 5A illustrates a diagrammatical representation of an exemplary weldbead with a single wire and FIG. 5B illustrates a diagrammaticalrepresentation of an exemplary weld bead with an embodiment of theinvention;

FIG. 6 illustrates a diagrammatical representation of an exemplary weldprocess flow chart for an embodiment of the present invention;

FIG. 7 illustrates a diagrammatical representation of an alternativeembodiment of a contact tip assembly for use with embodiments of thepresent invention;

FIG. 8 illustrates a diagrammatical representation of an exemplary weldcurrent waveform for embodiments of the present invention;

FIG. 9 illustrates a diagrammatical representation of a furtherexemplary weld current waveform for embodiments of the presentinvention; and

FIG. 10 illustrates a diagrammatical representation of an additionalexemplary weld current waveform for embodiments of the presentinvention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Exemplary embodiments of the invention will now be described below byreference to the attached Figures. The described exemplary embodimentsare intended to assist the understanding of the invention, and are notintended to limit the scope of the invention in any way. Like referencenumerals refer to like elements throughout.

While embodiments of the present invention discussed herein arediscussed in the context of GMAW type welding, other embodiments or theinvention are not limited thereto. For example, embodiments can beutilized in SAW and FCAW type welding operations, as well as othersimilar types of welding operations. Further, while the electrodesdescribed herein are solid electrodes, again, embodiments of the presentinvention are not limited to the use of solid electrodes as coredelectrodes (either flux or metal cored) can also be used withoutdeparting from the spirit or scope of the present invention. Further,embodiments of the present invention can also be used in manual,semi-automatic and robotic welding operations. Because such systems arewell known, they will not be described in detail herein.

Turning now to the Figures, FIG. 1 depicts an exemplary embodiment of awelding system 100 in accordance with an exemplary embodiment of thepresent invention. The welding system 100 contains a welding powersource 109 which is coupled to both a welding torch 111 (having acontact tip assembly—not shown) and a wire feeder 105. The power source109 can be any known type of welding power source capable of deliverythe current and welding waveforms described herein, for example, pulsespray, STT and/or short arc type welding waveforms. Because theconstruction, design and operation of such power supplies are wellknown, they need not be described in detail herein. It is also notedthat welding power can be supplied by more than one power supply at thesame time—again the operation of such systems are known. The powersource 109 can also include a controller 120 which is coupled to a userinterface to allow a user to input control or welding parameters for thewelding operation. The controller 120 can have a processor, CPU, memoryetc. to be used to control the operation of the welding process asdescribed herein. The torch 111, which can be constructed similar toknown manual, semi-automatic or robotic welding torches can be coupledto any known or used welding gun and can be of a straight or goosenecktype as described above. The wire feeder 105 draws the electrodes E1 andE2 from electrode sources 101 and 103, respectively, which can be of anyknown type, such as reels, spools, containers or the like. The wirefeeder 105 is of a known construction and employs feed rolls 107 to drawthe electrodes E1 and E2 and push the electrodes to the torch 111. In anexemplary embodiment of the present invention, the feed rolls 107 andwire feeder 105 are configured for a single electrode operation.Embodiments of the present invention, using a dual wire configuration,can be utilized with a wire feeder 105 and rollers 107 only designed fora single wire feeding operation. For example, rollers 107 can beconfigured for a single 0.045 inch diameter electrode, but will suitabledrive two electrodes of a 0.030 inch diameter without modification tothe wire feeder 105 or the rollers 107. Alternatively, the wire feeder105 can be designed to provide separate sets of rollers for feeding theelectrodes E1/E2 respectively. In other embodiments, two separate wirefeeders can also be used. As shown, the wire feeder(s) 105 is incommunication with the power source 109 consistent with knownconfigurations of welding operations.

Once driven by the rollers 107, the electrodes E1 and E2 are passedthrough a liner 113 to deliver the electrodes E1 and E2 to the torch111. The liner 113 is appropriately sized to allow for the passage ofthe electrodes E1 and E2 to the torch 111. For example, for two 0.030inch diameter electrodes, a standard 0.0625 inch diameter liner 113(which is typically used for a single 0.0625 inch diameter electrode)can be used with no modification.

Although the examples referenced above discuss the use of two electrodeshaving a same diameter, the present invention is not limited in thisregard as embodiments can use electrodes of a different diameter. Thatis, embodiments of the present invention can use an electrode of afirst, larger, diameter and an electrode of a second, smaller, diameter.In such an embodiment, it is possible to more conveniently weld two workpieces of different thicknesses. For example, the larger electrode canbe oriented to the larger work piece while the smaller electrode can beoriented to the smaller work piece. Further, embodiments of the presentinvention can be used for many different types of welding operationsincluding, but not limited to, metal inert gas, submerged arc, andflux-cored welding. Further, embodiments of the present invention can beused for automatic, robotic and semi-automatic welding operations.Additionally, embodiments of the present invention can be utilized withdifferent electrode types. For example, it is contemplated that a coredelectrode can be coupled with a non-cored electrode. Further, electrodesof differing compositions can be used to achieve the desired weldproperties and composition of the final weld bead. Thus, embodiments ofthe present invention can be utilized a broad spectrum of weldingoperations.

FIG. 2 depicts an exemplary contact tip assembly 200 of the presentinvention. The contact tip assembly 200 can be made from known contacttip materials and can be used in any known type of welding gun. As shownin this exemplary embodiment, the contact tip assembly has two separatechannels 201 and 230 which run the length of the contact tip assembly200. During welding a first electrode E1 is passed through the firstchannel 201 and the second electrode E2 is passed through the secondchannel 203. The channels 201/203 are typically sized appropriately forthe diameter of wire that is to be passed there through. For example, ifthe electrodes are to have the same diameter the channels will have thesame diameters. However, if different diameters are to be used then thechannels should be sized appropriately so as to properly transfercurrent to the electrodes. Additionally, in the embodiment shown, thechannels 201/203 are configured such that the electrodes E1/E2 exit thedistal end face of the contact tip 200 in a parallel relationship.However, in other exemplary embodiments the channels can be configuredsuch that the electrodes E1/E2 exit the distal end face of the contacttip such that an angle in the range of +/−15° exists between thecenterlines of the respective electrodes. The angling can be determinedbased on the desired performance characteristics of the weldingoperation. It is further noted that in some exemplary embodiments thecontact tip assembly can be a single integrated with a channels asshown, while in other embodiments the contact tip assembly can becomprised of two contact tip subassemblies located close to each other,where the current is directed to each of the contact tip subassemblies.

As shown in FIG. 2, the respective electrodes E1/E2 are spaced by adistance S which is the distance between the closest edges of theelectrodes. In exemplary embodiments of the present invention, thisdistance is in the range of 1 to 4 times the diameter of the larger ofthe two electrodes E1/E2, while in other exemplary embodiments thedistance S is in the range of 2 to 3 times the largest diameter. Forexample, if each of the electrodes has a diameter of 1 mm, the distanceS can be in the range of 2 to 3 mm. Further, in manual or semi-automaticwelding operations the distance S can be in the range of 1.75 to 2.25times the largest electrode diameter, whereas in robotic weldingoperations the distance S can be in the range of 2.5 to 3.5 times thelargest electrode diameter. In exemplary embodiments, the distance S isin the range of 1.5 to 3.5 mm.

As explained further below, the distance S should be selected to ensurethat a single bridge droplet is formed between the electrodes, beforethe droplet is transfer, while preventing the electrodes from contactingeach other, other than through the bridge droplet.

FIG. 3A depicts an exemplary embodiment of the present invention, whileshowing in the interactions of the magnetic forces from the respectiveelectrodes E1 and E2. As shown, due to the flow of current, a magneticfield is generated around the electrodes which tends to create a pinchforce that draws the wires towards each other. This magnetic force tendsto create a droplet bridge between the two electrodes, which will bediscussed in more detail below.

FIG. 3B shows the droplet bridge that is created between the twoelectrodes. That is, as the current passing through each of theelectrodes melts the ends of the electrodes the magnetic forces tend todraw the molten droplets towards each other until they connect with eachother. The distance S is far enough such that the solid portions of theelectrodes are not drawn to contact each other, but close enough that adroplet bridge is created before the molten droplet is transferred tothe weld puddle created by the welding arc. The droplet is depicted inFIG. 3C where the droplet bridge creates a single large droplet that istransferred to the puddle during welding. As show, the magnetic pinchforce acting on the droplet bridge acts to pinch off the droplet similarto the use of pinch force in a single electrode welding operation.

Further, FIG. 4A depicts an exemplary representation of current flow inan embodiment of the present invention. As shown the welding current isdivided so as to flow through each of the respective electrodes andpasses to and through the bridge droplet as it is formed. The currentthen passes from the bridge droplet to the puddle and work piece. Inexemplary embodiments where the electrodes are of the same diameter andtype the current will be essentially divided evenly through theelectrodes. In embodiments where the electrodes have differentresistance values, for example due to different diameters and/orcompositions/construction, the respective currents will be apportioneddue to the relationship of V=I*R, as the welding current is applied tothe contact tip similar to known methodologies and the contact tipprovides the welding current to the respective electrodes via thecontact between the electrodes and the channels of the contact tip. FIG.4B depicts the magnetic forces within the bridge puddle that aid increating the bridge droplet. As shown, the magnetic forces tend to pullthe respective molten portions of the electrodes towards each otheruntil they contact with each other.

FIG. 5A depicts an exemplary cross-section of a weld made with a singleelectrode welding operation. As shown, while the weld bead WB is of anappropriate width, the finger F of the weld bead WB, which penetratesinto the workpieces W as shown, has a relatively narrow width. This canoccur in single wire welding operations when higher deposit rates areused. That is, in such welding operations the finger F can become sonarrow that it is not reliable to assume that the finger penetrated inthe desired direction, and thus cannot be a reliable indicator of properweld penetration. Further, as this narrow finger dives deeper this canlead to defects such as porosity trapped near the finger. Additionally,in such welding operations the useful sides of the weld bead are not asdeeply penetrated as desired. Thus, in certain applications thismechanical bond is not as strong as desired. Additionally, in somewelding applications, such as when welding horizontal fillet welds, theuse of a single electrode made it difficult to achieve equal sized weldlegs, at high deposition speeds, without the addition of too much heatto the welding operation. These issues are alleviated with embodimentsof the present invention which can reduce the penetration of the fingerand spread the finger making the side penetration of the weld wider. Anexample of this is shown in FIG. 5B, which shows a weld bead of anembodiment of the present invention. As shown in this embodiment, asimilar, or improved weld bead leg symmetry and/or length can beachieved, as well as a wider weld bead at the weld depth within the weldjoint. This improved weld bead geometry is achieved while using lessoverall heat input into the weld. Therefore, embodiments of the presentinvention can provide improved mechanical weld performance with loweramounts of heat input, and at improved deposition rates.

FIG. 6 depicts a flow chart 600 of an exemplary welding operation of thepresent invention. This flow chart is intended to be exemplary and isnot intended to be limiting. As shown, a welding current/output isprovided by the welding power source 610 such that current is directedto the contact tip and electrodes consistent with known systemconstructions. Exemplary waveforms are discussed further below. Duringwelding a bridge droplet is allowed to form 620 between the electrodeswhere the respective droplets from each electrode contact each other tocreate a bridge droplet. The bridge droplet is formed prior tocontacting the weld puddle. During formation of the bridge droplet atleast one of a duration or a droplet size is detected until such time asthe droplet reaches a size to be transferred, and then the droplet istransferred to the puddle 640. The process is repeated during thewelding operation. To control the welding process the power sourcecontroller/control system can use either one of a bridge droplet currentduration and/or a bridge droplet size detection to determine if thebridge droplet is of a size to be transferred. For example, in oneembodiment a predetermined bridge current duration is used for a givenwelding operation such that a bridge current is maintained for thatduration, after which droplet transfer is then initiated. In a furtherexemplary embodiment, the controller of the power source/supply canmonitor the welding current and/or voltage and utilize a predeterminedthreshold (for example a voltage threshold) for a given weldingoperation. For example, in such embodiments, as the detected arc voltage(detected via a known type of arc voltage detection circuit) detectsthat the arc voltage has reached a bridge droplet threshold level thepower supply initiates a droplet separation portion of the weldingwaveform. This will be discussed further below in some exemplaryembodiments of welding waveforms that can be used with embodiments ofthe present invention.

FIG. 7 depicts an alternative exemplary embodiment of a contact tip 700that can be used with embodiments of the present invention. As describedpreviously, in some embodiments the electrodes can be directed to thetorch via a single wire guide/liner. Of course, in other embodiments,separate wire guide/liners can be used. However, in those embodiments,where a single wire guide/liner is used the contact tip can be designedsuch that the electrodes are separated from each other within thecontact tip. As shown in FIG. 7, this exemplary contact tip 700 has asingle entrance channel 710 with a single orifice at the upstream end ofthe contact tip 700. Each of the electrodes enter the contact tip viathis orifice and pass along the channel 710 until they reach aseparation portion 720 of the contact tip, where the separation portiondirects one electrode into a first exit channel 711 and a secondelectrode into the second exit channel 712, so that the electrodes aredirected to their discrete exit orifices 701 and 702, respectively. Ofcourse, the channels 710, 711 and 712 should be sized appropriately forthe size of electrodes to be used, and the separation portion 720 shouldbe shaped so as to not scar or scratch the electrodes. As shown in FIG.7, the exit channels 711 and 712 are angled relative to each other,however, as shown in FIG. 2, these channels can also be orientedparallel to each other.

Turning now to FIGS. 8 through 10, various exemplary waveforms that canbe used with exemplary embodiments of the present invention aredepicted. In general, in exemplary embodiments of the present invention,the current is increased to create the bridge droplet and build it fortransfer. In exemplary embodiments, at transfer the bridge droplet hasan average diameter which is similar to the distance S between theelectrodes, which can be larger than the diameter of either of theelectrodes. When the droplet is formed it is transferred via a high peakcurrent, after which the current drops to a lower (e.g. background)level to remove the arc pressure acting on the wires. The bridgingcurrent then builds the bridge droplet without exerting too much pinchforce to pinch off the developing droplet. In exemplary embodiments,this bridging current is at a level in the range of 30 to 70% betweenthe background current and the peak current. In other exemplaryembodiments, the bridging current is in the range of 40 to 60% betweenthe background current and the peak current. For example, if thebackground current is 100 amps and the peak current is 400 amps, thebridging current is in the range of 220 to 280 amps (i.e., 40 to 60% ofthe 300 amp difference). In some embodiments the bridging current can bemaintained for a duration in the range of 1.5 to 8 ms, while in otherexemplary embodiments the bridging current is maintained for a durationin the range of 2 to 6 ms. In exemplary embodiments the bridging currentduration begins at the end of the background current state and includesthe bridging current ramp up, where the ramp up can be in the range of0.33 to 0.67 ms depending on the bridging current level and the ramprate. With exemplary embodiments of the present invention, the pulsefrequency of waveforms can be slowed down as compared to single wireprocesses to allow for droplet growth which can improve control andallow for higher deposition rates as compared to single wire operations.

FIG. 8 depicts an exemplary current waveform 800 for a pulsed spraywelding type operation. As shown, the waveform 800 has a backgroundcurrent level 810, which then transitions to a bridge current level 820,during which the bridge droplet is grown to a size to be transferred.The bridge current level is less than a spray transition current level840 at which the droplet starts its transfer to the puddle. At theconclusion of the bridge current 820 the current is raised to beyond thespray transition current level 840 to a peak current level 830. The peakcurrent level is then maintained for a peak duration to allow for thetransfer of the droplet to be completed. After transfer the current isthen lowered to the background level again, as the process is repeated.Thus, in these embodiments the transfer of the single droplet does notoccur during the bridge current portion of the waveform. In suchexemplary embodiments, the lower current level for the bridge current820 allows a droplet to form without excessive pinching force to directthe droplet to the puddle. Because of the use of the bridge droplet,welding operations can be attained where the peak current 830 can bemaintained for a longer duration at a higher level than using a singlewire. For example, some embodiments can maintain the peak duration forat least 4 ms, and in the range of 4 to 7 ms, at a peak current level inthe range of 550 to 700 amps, and a background current in the range of150 to 400 amps. In such embodiments, a significantly improveddeposition rate can be achieved. For example, some embodiments haveachieved deposition rates in the range of 19 to 26 lbs/hr, whereassimilar single wire processes can only achieve a deposition rate in therange of 10 to 16 lbs/hr. For example, in one non-limiting embodiment apair of twin wires having a diameter of 0.040″, using a peak current of700 amps, a background current of 180 amps and a droplet bridge currentof 340 amps can be deposited at a rate of 19 lb/hr at a frequency of 120Hz. Such a deposition is at a frequency much less than conventionalwelding processes, and thus more stable.

FIG. 9 depicts another exemplary waveform 900 that can be used in ashort arc type welding operation. Again, the waveform 900 has abackground portion 910 prior to a short response portion 920 which isstructured to clear a short between the droplet and the puddle. Duringthe shorting response 920 the current is raised to clear the short andas the short is cleared the current is dropped to a bridge current level930 during which the bridge droplet is formed. Again, the bridge currentlevel 930 is less than the peak current level of the shorting response920. The bridge current level 930 is maintained for a bridge currentduration that allows a bridge droplet to be formed and directed to thepuddle. During transfer of the droplet current is then dropped to thebackground level, which allows the droplet to advance until a shortoccurs. When a short occurs the shorting response/bridge currentwaveform is repeated. It should be noted that in embodiments of thepresent invention it is the presence of the bridge droplet that makesthe welding process more stable. That is, in traditional weldingprocesses that use multiple wires there is no bridge droplet. In thoseprocesses when one wire shorts or makes contact with the puddle the arcvoltage drops and the arc for the other electrode will go out. This doesnot occur with embodiments of the present invention, where the bridgedroplet is common to each of the wires.

FIG. 10 depicts a further exemplary waveform 1000, which is a STT(surface tension transfer) type waveform. Because such waveforms areknown, they will not be described in detail herein. To further explainan STT type waveform, its structure, use and implementation, US.Publication No. 2013/0264323, filed on Apr. 5, 2012, is incorporatedherein in its entirety. Again, this waveform has a background level1010, and a first peak level 1015 and a second peak level 1020, wherethe second peak level is reached after a short between the droplet andpuddle is cleared. After the second peak current level 1020, the currentis dropped to a bridge current level 1030 where the bridge droplet isformed, after which the current is dropped to the background level 1010to allow the droplet to be advanced to the puddle, until it makescontact with the puddle. In other embodiments, an AC waveform can beused, for example an AC STT waveform, pulse waveform, etc. can be used.

The use of embodiments described herein can provide significantimprovements in stability, weld structure and performance over knownwelding operations. However, in addition to welding operations,embodiments can be used in additive manufacturing operations. In factthe system 100 described above can be used in additive manufacturingoperations as in welding operations. In exemplary embodiments, improveddeposition rates can be achieved in additive manufacturing operations.For example, when using an STT type waveform a single wire additiveprocess, using an 0.045″ wire can provide a deposition rate of about 5lb/hr before becoming unstable. However, when using embodiments of thepresent invention and two 0.040″ wires a deposition rate of 7 lbs/hr canbe achieved in a stable transfer. Because additive manufacturingprocesses and systems are known, the details of which need not bedescribed herein. In such processes a bridging current, such as thatdescried above, can be used in the additive manufacturing currentwaveform.

It is noted that exemplary embodiments are not limited to the usage ofthe waveforms discussed above and described herein, as other weldingtype waveforms can be used with embodiments of the present invention.For example, other embodiments can use variable polarity pulsed spraywelding waveforms, AC waveforms, etc. without departing from the spiritand scope of the present invention. For example, in variable polarityembodiments the bridge portion of the welding waveform can be done in anegative polarity such that the bridge droplet is created while reducingthe overall heat input into the weld puddle. For example, when using ACtype waveforms, the waveforms can have a frequency of 60 to 200 Hz ofalternating negative and positive pulses to melt the two wires and formthe bridge droplet between them. In further embodiments the frequencycan be in the range of 80 to 120 Hz.

As explained previously, embodiments of the present invention can beused with different types and combinations of consumables including fluxcored consumables. In fact, embodiments of the present invention canprovide a more stable welding operation when using flux coredelectrodes. Specifically, the use of a bridging droplet can aid instabilizing flux core droplets that can tend to be unstable in a singlewire welding operation. Further, embodiments of the present inventionallow for increased weld and arc stability at higher deposition rates.For example, in single wire welding operations, at high current and highdeposition rates the transfer type for the droplets can change fromstreaming spray to a rotational spray, which appreciably reduces thestability of the welding operation. However, with exemplary embodimentsof the present invention the bridge droplet stabilizes the dropletswhich significantly improves arc and weld stability at high depositionrates, such as those above 20 lb/hr.

Additionally, as indicated above the consumables can be of differenttypes and/or compositions, which can optimize a given welding operation.That is, the use of two different, but compatible, consumables can becombined to create a desired weld joint. For example, compatibleconsumables include hardfacing wires, stainless wires, nickel alloys andsteel wires of different composition can be combined. As one specificexample a mild steel wire can be combined with an overalloyed wire tomake a 309 stainless steel composition. This can be advantageous when asingle consumable of the type desired does not have desirable weldproperties. For example, some consumables for specialized weldingprovide the desired weld chemistry but are extremely difficult to useand have difficulty providing a satisfactory weld. However, embodimentsof the present invention allow for the use of two consumables that areeasier to weld with to be combined to create the desired weld chemistry.Embodiments of the present invention can be used to create analloy/deposit chemistry that is not otherwise commercially available, orotherwise very expensive to manufacture. Thus, two different consumablescan be used to obviate the need for an expensive or unavailableconsumable. Further, embodiments can be used to create a diluted alloy,for example, the first wire is a common inexpensive alloy and the secondis wire is a specialty wire. The desired deposit would be the average ofthe two wires, mixed well in the formation of the bridged droplet, atthe lower average cost of the two wires, over an expensive specialtywire. Further, in some applications, the desired deposit could beunavailable due to the lack of appropriate consumable chemistry, butcould be reached by mixing two standard alloy wires, mixed within thebridged droplet and deposited as a single droplet. Further, in someapplications, such as the application of wear resistance metals, thedesired deposit may be combination of tungsten carbide particles fromone wire and chrome carbide particles from another. Still in anotherapplication, a larger wire housing larger particles within is mixed witha smaller wire containing less particles or smaller particles is used todeposit a mixture of the two wires. Here the expected contribution fromeach of the wires is proportional to the size of wire given the wirefeed speeds are same. In yet another example, the wire feed speeds ofthe wires is different to allow the alloy produced to change based onthe desired deposit but the mixing of the wires is still produced by thebridged droplet created between the wires.

While the invention has been particularly shown and described withreference to exemplary embodiments thereof, the invention is not limitedto these embodiments. It will be understood by those of ordinary skillin the art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the invention as definedby the following claims.

What is claimed is:
 1. A welding or additive manufacturing system,comprising: a power supply with a controller, where said power supplyoutputs a current waveform; and a contact tip assembly having a firstand second exit orifice, where said contact tip assembly is configuredto direct a first consumable through said first exit orifice to adeposition operation and a second consumable through said second exitorifice to said deposition operation, and where said contact tipassembly is configured such that a distance S exists between said firstand second consumables as measured at each of the respective first andsecond exit orifices; wherein said current waveform has a peak currentlevel, a background current level and a bridging current level; whereinsaid bridging current level is configured to form a bridging dropletwhich couples said first and second consumables before said bridgingdroplet is transferred to a puddle during said deposition operation,wherein solid portions of the first consumable delivered through thefirst exit orifice are spaced apart from solid portions of the secondconsumable delivered through the second exit orifice during saiddeposition operation, and wherein a current due to said current waveformflows from said contact tip assembly to the bridging droplet throughboth of the first consumable and the second consumable and the currentis divided between the first consumable and the second consumable, andwherein the current flows from the bridging droplet to the puddle. 2.The system of claim 1, wherein said bridging current level is in therange of 30 to 70% of the difference between said peak current level andsaid background current level.
 3. The system of claim 1, wherein saidbridging current level is in the range of 40 to 60% of the differencebetween said peak current level and said background current level. 4.The system of claim 1, wherein said peak current level is maintained forat least 4 ms.
 5. The system of claim 1, wherein said peak current levelis maintained for a duration in the range of 4 to 7 ms.
 6. The system ofclaim 1, wherein said peak current level is in the range of 550 to 700amps.
 7. The system of claim 1, wherein said bridging current level ismaintained for a predetermined bridge current duration.
 8. The system ofclaim 1, wherein said bridging current level is maintained for a bridgecurrent duration in the range of 1.5 to 8 ms.
 9. The system of claim 1,wherein said bridging current level is maintained for a bridge currentduration in the range of 2 to 6 ms.
 10. The system of claim 1, whereinsaid controller initiates transfer of said bridging droplet after abridge droplet threshold level is reached during said depositionoperation.
 11. A method of welding or additive manufacturing,comprising: providing a current waveform to a contact tip assemblyhaving a first exit orifice and second exit orifice, where said currentwaveform has a peak current level, a background current level and abridging current level, providing a first consumable to said contact tipassembly such that said first consumable exits said first exit orifice;providing a second consumable to said contact tip assembly such thatsaid second consumable exits said second exit orifice, where said firstand second exit orifices are positioned from each other such that adistance S exists between said first and second consumables; forming abridging droplet between said first and second consumables during saidbridging current level, while preventing solid portions of the firstconsumable delivered through the first exit orifice from contactingsolid portions of the second consumable delivered through the secondexit orifice during a deposition operation, where said bridging dropletcouples said first and second consumables before said bridging dropletis transferred to a puddle during said deposition operation, wherein acurrent due to said current waveform flows from said contact tipassembly to the bridging droplet through both of the first consumableand the second consumable and the current is divided between the firstconsumable and the second consumable, and wherein the current flows fromthe bridging droplet to the puddle.
 12. The method of claim 11, whereinsaid bridging current level is in the range of 30 to 70% of thedifference between said peak current level and said background currentlevel.
 13. The method of claim 11, wherein said bridging current levelis in the range of 40 to 60% of the difference between said peak currentlevel and said background current level.
 14. The method of claim 11,wherein said peak current level is maintained for at least 4 ms.
 15. Themethod of claim 11, wherein said peak current level is maintained for aduration in the range of 4 to 7 ms.
 16. The method of claim 11, whereinsaid peak current level is in the range of 550 to 700 amps.
 17. Themethod of claim 11, wherein said bridging current level is maintainedfor a predetermined bridge current duration.
 18. The method of claim 11,wherein said bridging current level is maintained for a bridge currentduration in the range of 1.5 to 8 ms.
 19. The method of claim 11,wherein said bridging current level is maintained for a bridge currentduration in the range of 2 to 6 ms.
 20. The method of claim 11, whereinsaid controller initiates transfer of said bridging droplet after abridge droplet threshold level is reached during said depositionoperation.
 21. A welding or additive manufacturing system, comprising: apower supply with a controller, where said power supply outputs acurrent waveform; and a single contact tip having a first exit orificeand a second exit orifice, where said single contact tip is configuredto direct a first consumable through said first exit orifice and asecond consumable through said second exit orifice, and where saidsingle contact tip is configured such that a distance S exists betweensaid first and second consumables as measured at each of the respectivefirst and second exit orifices; wherein said current waveform has a peakcurrent level, a background current level, and a bridging current level,wherein said distance S and said bridging current level are togetherconfigured to form a bridge droplet which couples said first and secondconsumables prior to contacting a puddle during a deposition operation,wherein solid portions of the first consumable delivered through thefirst exit orifice are spaced apart from solid portions of the secondconsumable delivered through the second exit orifice during saiddeposition operation, and wherein a current due to said current waveformflows from said single contact to the bridge droplet through both of thefirst consumable and the second consumable and the current is dividedbetween the first consumable and the second consumable, and wherein thecurrent flows from the bridge droplet to the puddle.